Improvements will be sought in the widely used Ames' Salmonella strains for the detection of mutagens/carcinogens. The hope is that the sensitivity and scope of mutagen detection, which are already high, will be still further improved and extended. Evidence for the action of nitrous acid in causing novel mutagenic DNA lesions (intrastrand cross-links) will be sought by treatment and analysis of synthetic polymers. Possible monoclonality of foci of intestinal metaplasia (spots of intestinal tissue located in the stomach) will be investigated using two systems: (a) Mutagen-treated female mice polymorphic at the X-linked PGK locus, and (b) Human waste tissues from females heterozygous at the X-linked G6PD locus. Additional reagents will be prepared to facilitate ready recognition and characterization of metaplasias.